Ultrasonic flow meters using ultrasonic wave have been known as one type of conventional flow meters for measuring a flow rate of a fluid that flows through a pipe line.
Of these, an ultrasonic flow meter having a measuring unit configured using a straight tube as a tubular body for measurement through which a fluid for measuring a flow rate flows is generally called as a straight tube ultrasonic flow meter. The measuring unit of the straight tube ultrasonic flow meter is configured such that a pair of oscillators (ultrasonic transducers) are disposed around an outer circumference of a tubular body for measurement as a straight tube at a predetermined interval along an axial (longitudinal) direction.
Such a straight tube ultrasonic flow meter causes one of the oscillators to transmit ultrasonic wave and the other oscillator to receive the transmitted ultrasonic wave at the same time as causing the other oscillator to transmit ultrasonic wave and the one oscillator to receive the transmitted ultrasonic wave, obtains a flow velocity of a fluid within the tubular body for measurement based on a difference occurring in propagation time of the ultrasonic wave, and thereby measures a flow rate of the fluid based on the flow velocity.
Examples of the ultrasonic flow meter described above include a straight tube ultrasonic flow meter, as described in PTL 1, using a straight tube without any bent portion as a tubular body for measurement on which a pair of oscillators are disposed to configure a measuring unit.